Ball Grid Array (BGA) is an advanced type of semiconductor packaging technology which is characterized by the use of a substrate whose front surface is mounted with one or more semiconductor dice and whose back surface is planted with an array of solder balls. During Surface Mount Technology (SMT) process, the BGA package is mechanically bonded and electrically coupled to an external printed circuit board via these solder balls.
Flip-Chip Ball Grid Array (FCBGA) is a more advanced type of BGA technology which is characterized by that the packaged semiconductor die is mounted in an upside-down manner (i.e., flip chip) over the substrate and bonded to the same by means of a plurality of solder bumps attached to the I/O pads thereon. FCBGA technology needs no wires to electrically connect the semiconductor die to the substrate, so as to minimize size of the BGA package.
FIG. 1 is a schematic diagram showing a cross-sectional view of a typical FCBGA-type of semiconductor package with heat spreader. As shown in FIG. 1, the FCBGA package is composed of: (a) a substrate 10; (b) at least one semiconductor die 20; (c) an adhesive layer 30; (d) a heat spreader 40; and (e) an array of solder balls (i.e., ball grid array) 50.
The substrate 10 has a front surface 10a and a back surface 10b, and whose front surface 10a is defined by design into a die mounting area 11 and a heat spreader attach area 12. The die mounting area 11 of the substrate 10 is used for mounting the semiconductor die 20 thereon in an upside-down manner (i.e., flip-chip). While the semiconductor die 20 is mounted in position, the heat spreader attach area 12 is coated with the adhesive layer 30 for mounting the heat spreader 40 thereon.
The heat spreader 40 includes an elevated overhead portion 41 and a support portion 42, and which is mounted over the front surface 10a of the substrate 10 in such a manner that the support portion 42 is adhered by means of the adhesive layer 30 to the heat spreader attach area 12 of the substrate 10, with its elevated overhead portion 41 coming into contact with the back side of the flip chip 20 (i.e., the inactive surface of the chip 20), preferably adhered by means of a thermally-conductive adhesive layer 21. Accordingly, the heat produced from the flip chip 20 during operation is transmitted to the heat spreader 40 and then dissipated via the heat spreader 40 to the atmosphere.
One shortcoming to the conventional FCBGA package depicted in FIG. 1, however, is that during fabrication or transporting, the heat spreader 40 would easily fall off position from the substrate 10, resulting in undesirable quality issue of the finished product. This problem is due to many causes, such as contaminant on the front surface 10a of the substrate 10, mismatch of CTE (Coefficient of Thermal Expansion) values between the heat spreader 40 and the substrate 10, thermal stress resulting in deformation, and crosswise shear stress (as indicated by Fx with arrow in FIG. 1) against the heat spreader 40 during transportation, and so on. When the heat spreader 40 falls off position from the substrate 10, the finished product of the FCBGA package undoubtedly regard as a defective one.
Related patents includes, for example, U.S. Pat. No. 5,459,368 entitled “Surface Acoustic Wave Device Mounted Module”; and U.S. Pat. No. 5,637,920 entitled “High Contact Density Ball Grid Array Package For Flip-chip”; to name just a few. However, these and other conventional patents provide no solutions to the aforementioned problems.